1. Field
The disclosed subject matter relates to flotation reagents and a froth flotation process for using the flotation reagents for the enhanced recovery of value sulfide minerals and precious metals from ores containing Mg-silicates, slime forming minerals and/or clays. More particularly, the disclosed subject matter relates to the use of certain modifiers, referred to as froth phase modifiers, either alone or with certain monovalent ion modifier enhancing agents and further in combination with certain collectors, and a flotation process using these reagents for the enhanced recovery of value sulfide minerals and precious metals from Mg-silicate containing ores, slime forming ores and/or clay containing ores.
2. Related Art
Froth flotation is a widely used process for beneficiating ores containing minerals and metals of interest, referred to as “value minerals”. The term value minerals is meant to include not only minerals of value, but also metals of value, such as copper and precious metals such as gold, silver, and platinum group metals, and combinations thereof. Certain theory and practice state that success of a flotation process for base metal sulfide and precious metal ores depends on reagents known as “collectors,” which impart selective hydrophobicity to the value mineral which is separated from other minerals. See U.S. Pat. No. 4,584,097 which is hereby incorporated herein by reference.
Other reagents, such as “frothers”, may be added to the process to provide a suitable basic froth phase to capture hydrophobic value minerals and facilitate separation and recovery thereof. Certain other reagents, referred to as “modifiers” in a broad sense, may be used to enhance separation and recovery of value minerals and metals. Modifiers which can include pH regulators may be used to modify and control pH of the ore pulp in order to enhance separation and recovery of value mineral. In some instances, activators, such as copper sulfate, may be used to activate a certain value sulfide mineral in order to enhance collector coating on this sulfide mineral. Certain other modifiers also contribute to successful flotation separation of the value sulfides and precious metals. See U.S. Pat. No. 5,531,330, which is incorporated herein by reference. Modifiers include, but are not necessarily limited to, all reagents whose principal function is neither collecting nor frothing, but can typically be used to modify the surface of the mineral so that it does not float. Additionally, modifiers can be used to modify water chemistry, the surface of the froth bubbles and are generally used to optimize the conditions for floating a chosen value mineral or metal. In addition to attempts at making collectors more selective for value sulfide minerals and precious metals, modifiers can also be used to address the problem of improving the flotation separation of value sulfide minerals and precious metals as depressants or dispersants, to prevent or reduce non-sulfide gangue minerals reporting to the concentrate of mineral and metal values. A depressant is a modifier reagent which acts selectively on certain unwanted minerals and prevents or inhibits their flotation. A dispersant is a modifier reagent that functions substantially similar to the depressant, but it may also reduce the slurry viscosity and disperse fines or slimes and other functions.
Certain other modifier reagents as discussed herein are referred to as “froth phase modifiers.” As used herein, the term “froth phase modifier” means any reagent that may improve the properties of the froth phase and thereby enhance separation and recovery of value minerals, as well as reagents that may have beneficial effects in the pulp or slurry phase such as viscosity reduction of the slurry, depression or dispersion of certain silicates, and the like. The term “froth phase modifier” also encompasses reagents that have more than one function or purpose in the froth flotation process, e.g., act as a modifier of the froth phase and a depressant or dispersant.
It is widely accepted that the presence of certain non-sulfide silicate gangue minerals such as Mg-bearing silicates, slime-forming minerals and/or clays in certain sulfide mineral and precious metal ores may be problematic due to their adverse effects on value mineral separation and recovery even if very selective value mineral collectors are used. Examples of such silicates include, but are not limited to: serpentines, amphiboles, actinolite, chrysotile, tremolite, biotite, lizardite, antigorite, chlorite, sericite, and clay minerals. These silicates are often present in Mg-containing ores, slime forming ores and clay containing ores. Certain other Mg-bearing silicates, known as “naturally hydrophobic Mg-silicates,” such as talc and pyrophyllite, may also be present in these ores. The naturally hydrophobic Mg-silicates are also problematic in view of their significant natural floatability.
Reagents that selectively depress naturally hydrophobic Mg-silicates are known in the art, and examples include polysaccharides such as guar gum, carboxymethyl cellulose, and polymers such as those disclosed in U.S. Pat. Nos. 5,531,330 and 5,533,626 and references therein. The reagents known to selectively depress naturally hydrophobic Mg-silicates are often found to be less effective for depressing the above-mentioned Mg-bearing silicates, slime-forming minerals and/or clays in Mg-containing ores, slime forming ores and clay containing ores. As a result, when a complex mixture of silicates is present in an ore, these known reagents do not yield sufficient improvement in value mineral separation and recovery. In other words, merely depressing naturally hydrophobic Mg-silicates, such as talc and pyrophyllite, may not be sufficient to obtain desired metallurgical performance. Many other reagents have been disclosed in the art as depressants or dispersants to alleviate problems associated with the non-hydrophobic Mg silicates, slimes and/or clays in both sulfide and non-sulfide mineral flotation separation systems.
In addition to poor or inadequate recovery of value minerals, the value mineral concentrate grades are often lowered by the presence of Mg-bearing silicates, slime-forming minerals and/or clays in Mg-silicate containing ores, slime forming ores and clay containing ores, which a) add to the cost of handling and transportation of the concentrate, b) compete for space in the froth phase during the flotation stage, thereby reducing the overall value mineral recovery, c) adversely affect the froth phase properties, thereby decreasing efficiency of separation in the froth phase, and d) create a significant problem in subsequent smelting of concentrates by increasing slag viscosity requiring higher operating temperature or causing significant metal losses to the slag.
The severity of the effect of silicates is believed to be influenced by the type, morphology and the amount of the silicates present in the ore. The adverse effects have been attributed to several factors including, for example, the tendency of silicate minerals to form a complex network structure in the pulp or slurry phase leading to a significant increase in pulp or slurry viscosity, which somehow hinders the separation of value minerals from the gangue silicate minerals. Another proposed theory is the formation of a coating of these silicates on the value minerals, thus blinding them to the collector action which in turn affects the separation, a phenomenon commonly described in the art as “slime coating”.
Although the inventors do not subscribe to or wish to be bound by any of the proposed theories, in some systems containing certain silicates, there appears to be no noticeable effect of these silicates on pulp phase properties, while there is a large adverse effect on froth phase properties, value mineral recovery and the grade of the concentrate. At times, it has also been observed that the value mineral recovery is not impacted at all, but the concentrate grade is adversely affected. In other systems, the presence of even a small amount of some of certain silicates, around 1-2%, may have an adverse effect on the value mineral recovery.
When the amount of the Mg-bearing silicates, slime-forming minerals and/or clays present in an ore is high (e.g. >0 to 80%), the pulp phase viscosity increases to such an extent that the processing of Mg-containing ores, slime forming ores and clay containing ores becomes challenging, thus rendering commonly used methods, processes and reagents inefficient. Well-known solutions to the problem are often inadequate and/or unattractive. For example, reduction of the percent of solids or slurry density to improve value mineral recovery and grade often suffers from several drawbacks, including, but not limited to: reduction of plant throughput and production, increase of consumption of water resources, reduction of comminution efficiency and insufficient improvement in value recovery or grade.
Another proposed solution has been the use of dispersants such as sodium silicate, soda ash, carboxymethyl cellulose, sodium poly phosphate, lignin sulfonate, and the like, which suffer from similar drawbacks as mentioned above. A further proposed solution has been making a size separation from the pulp or slurry prior to flotation. Thus, for example, the ground pulp or slurry is split into two size fractions: a sand (or coarse) fraction and a slime (or fines) fraction; or it is split into three size fractions: coarse, fine and slimes. US Patent Application Publication No. 20040217070 details one particular application of this concept that requires a large number of cyclones, significant capital and operational costs, and variability in size splits and plant performance. For some ores, even after desliming or size separation and treating the different size fractions separately, the overall performance improvement may be insufficient to justify implementing the solution.